/***** Big Number Subtraction *******************/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
#define MAX 10005
/*******************************************************************/
void reverse(char *from, char *to ){
    long len=strlen(from);
    long l;
    
    for(l=0;l<len;l++)
    to[l]=from[len-l-1];
    to[len]='\0';
}

int call_minus(char *large, char *small, char *result){
    char L[MAX], S[MAX];
    long l,s,now,hold,diff,sign=0;
    
    for(l=0;l<MAX;l++) L[l]=S[l]=0;
    l=strlen(large);
    s=strlen(small);
    if(l<s){
        strcpy(result,large);
        strcpy(large,small);
        strcpy(small,result);
        now=l; l=s; s=now;
        sign = 1;
    }
    if(l==s){
        if(strcmp(large, small)<0){
            strcpy(result,large);
            strcpy(large,small);
            strcpy(small,result);
            now=l; l=s; s=now;
            sign =1;
        }
    }
    reverse(large,L);
    reverse(small,S);
    for(;s<l;s++)
    S[s]='0';
    S[s]='\0';
    for(now=0,hold=0;now<l;now++){
        diff=L[now]-(S[now]+hold);
        if(diff<0){
             hold=1;
            result[now]=10+diff+'0';
        }
        else{
            result[now]=diff+'0';
            hold=0;
        }
    }
    for(now=l-1;now>0;now--){
        if(result[now]!='0')
        break;
    }
    result[now+1]='\0';
    reverse(result,L);
    strcpy(result,L);
    return sign;
}

int main(){
    char fir[MAX],sec[MAX],res[MAX];
    long len, test, i;
    
    while(scanf("%ld", &test)!=EOF){
        while(test--){
            for(i=0;i<MAX;i++) fir[i]=sec[i]=res[i]=0;
            scanf("%s%s",fir,sec);
            if(call_minus(fir,sec,res)==1) printf("-");
            len = strlen(res);
            for(i=0;i<len;i++) printf("%c",res[i]);
            printf("\n");
        }
    }
    
    return 0;
}
